The typical hard disk drive includes a head disk assembly (HDA) and a printed circuit board (PCB) attached to a disk drive base of the HDA. The head disk assembly includes at least one disk (such as a magnetic disk, magneto-optical disk, or optical disk), a spindle motor for rotating the disk, and a head stack assembly (HSA). The printed circuit board assembly includes electronics and firmware for controlling the rotation of the spindle and for controlling the position of the HSA, and for providing a data transfer channel between the disk drive and its host.
The spindle typically includes a rotor including one or more rotor magnets and a rotating hub on which disks are mounted and clamped, and a stator. If more than one disk is mounted on the hub, the disks are typically separated by spacer rings that are mounted on the hub between the disks. Various coils of the stator are selectively energized to form an electromagnetic field that pulls/pushes on the rotor magnet(s), thereby rotating the hub. Rotation of the spindle hub results in rotation of the mounted disks.
The head stack assembly typically includes an actuator, at least one head gimbal assembly (HGA), and a flex cable assembly. Each HGA includes a head for reading and writing data from and to the disk. In magnetic recording applications, the head typically includes an air bearing slider and a magnetic transducer that comprises a writer and a read element. The magnetic transducer's writer may be of a longitudinal or perpendicular design, and the read element of the magnetic transducer may be inductive or magnetoresistive. In optical and magneto-optical recording applications, the head may include a mirror and an objective lens for focusing laser light on to an adjacent disk surface. The head is adhered to a suspension assembly that includes a gimbal, load beam, bend region, and swage plate. The suspension acts to preload the head against the surface of the disk.
During operation of the disk drive, the actuator must rotate to position the HGAs adjacent desired information tracks on the disk. The actuator includes a pivot-bearing cartridge to facilitate such rotational positioning. The pivot-bearing cartridge fits into a bore in the body of the actuator. One or more actuator arms extend from the actuator body. An actuator coil is supported by the actuator body, and is disposed opposite the actuator arms. The actuator coil is configured to interact with one or more fixed magnets in the HDA, typically a pair, to form a voice coil motor. The printed circuit board assembly provides and controls an electrical current that passes through the actuator coil and results in a torque being applied to the actuator.
There is competitive pressure to continually develop hard disk drives that can access data more quickly, and so techniques are continuously being developed to decrease access time. One potential technique to accomplish this is to increase the rotational accelerations with which the head stack assembly is pivoted to position the head over a desired track of information on the disk. Unfortunately, higher rotational accelerations and applied torques on the actuator may lead to increased excitation of certain undesired vibration modes of the actuator. Externally applied mechanical shocks can also excite such actuator vibration modes.
In particular, if the frequency of the so-called “pivot butterfly mode” is too low, and/or if there is inadequate frequency separation between the pivot butterfly mode and the so-called “pivot rocking mode,” then the useful bandwidth of effective actuator control may be undesirably reduced. Thus, there is a need in the art for ways to increase the frequency of the pivot butterfly mode of a disk drive actuator, and/or to ensure adequate frequency separation between the pivot butterfly mode and the pivot rocking mode of a disk drive actuator.